Producing bronze powder pigments



Oct. 22, 1935. M BOQTHMAN 2,017,851

' PRODUCING BRONZE POWDER PIGMENTS Filed June 27, 1933 INVENZ'GR Da/e JZ 50076070 A TTORNEY Patented Oct. 22, 1935 v 2,017,851 PRODUCING BRONZE POWDER PIGMENTS Dale M. Boothman, Oakmont, Pa, assignor to Alumin um Company of America, Pittsburgh.

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Pa., a corporation of Pennsylv Application June 27, 1933, Serial No. 677,811 22 Claims. .(Cl. 134-76) This invention relates to the production of bronze powder pigments. It relates especially to the disintegration of'metals, such as aluminum, 1 into fine flakes adapted for use as bronze powder pigments in powder form or in paste form. More specifically, the invention relatesto an improved method of producing aluminum bronze powder the presence of a lubricant, and were usually followed by a polishing treatment designed to impart brilliance and good leaflng properties to the metal flakes. When processes of this nature are applied to aluminum, sheet or foil having a thickness of about 0.016 inch (about 26 gauge) or less is shredded or cut into small pieces and put through a rough stampmill or the like ,to reduce or disintegrate it into large, soft ductile flakes which constitute an intermediate product called shrode. This shrode is subjected to further stamping, whereby it is at least partially reduced to flne powder. The resulting product is screened or otherwise treated to separate the fine flakes from any coarse material which may be present, and the fine material is then, in some instances, ready for the market. For most purposes, however, and especially when thepowder is to be used as a pigment, a subsequent polishing treatment is necessary in order to produce a powder having the desired characteristics. The polishing operation and both of the stamping operations are inherently slow and laborious, and therefore relatively costly. When it is desired to market the bronze powder in paste form, the powder produced in a loose dry condition as described hereinabove must be mixed with the proper amount of a suitable vehicle until a paste of the desired consistency is obtained. This procedure is also slow and laborious in many instances.

In my copending application, Serial No. 597,- 901., filed March 10,1932, I have described an unproved method of producing shrode, which consists of coating aluminum sheet, foil, or scrap stamping operations.

said application that aluminum bronze powder can be produced by continuing the rolling of the shrode until the metal is disintegrated to a suitable fineness. Powder that is satisfactory for many purposes can be produced in this way, and 5 my discovery of this fact is a valuable contribution to the art of bronze powder making. However, powder produced by my'previously disclosed process sometimes required polishing or other treatment to improve its appearance and its suitno ability for certain applications. For example, I have found that when aluminum powder is produced by rolling under conditions that result in the production oi satisfactory shrode, thereis sometimes encountered a tendency on the part of 15 the finer flakes or particles to roll up together into pellets or agglomerates, or to break up into granular pieces before they have been rolled to the required thinness, which reduces the desirability of the powdered product for use as a pig- 2o ment. I a

The main object of my present invention is to provide an improved process of preparing fine, polished metal flakes or powders, in which the diificulties and disadvantages encountered in pre- 25 vious processes are avoided or overcome. Further specific objects of myinvention are to pro- -by rolling in the presence of sumcient lubricating material to form a cake with the metal partid0 cles. I have found that when the lubricant is present in the proper quantity, the thin flakes do not roll up into pellets when subjected to disin'tegratingtreatment in a rolling mill. Another advantage of my, new method of disintegration is ad that the surfaces-of the particles are polished sufficiently to make a separate and additional polishing operation unnecessary, even when producing powder-tor use as a pigment. A further advantageous result, which is perhaps even more 50 remarkable than those previously mentioned, is that the cake formed from the metal particles and the lubricant rolls readily, and behaves similarly to sheet metal in that it provides a "bite for the rolls, which makes it possible to so conduct the disintegration that powder of extreme thinness as well as fineness is produced. This is one of the important features which distinguish my present cake-forming process from previous processes, as loose or substantially dry bronze powder flows readily and provides no bite for the rolls, and becomes increasingly difficult to roll as its fineness increases.

- After the lubricant has been added to the shrode or other partially disintegrated metal and rolled or otherwiseintimately mixed therewith to coat all the particles and hold them, without welding together, in the form of a cake, the consistency of the cake is not usually changed materially by subsequent disintegrating passes through the rolls; and when the disintegration is completed the product is in the form of a cake or thick batter. This represents a new and highly useful intermediate product in the bronze powder art, and may be readily "converted into a high grade loose bronze powder, or into a bronze powder paste, as willbe described in detailhereinbelow.

' In carrying out my improved process, the choice of a proper lubricant is important. By the term lubricant" as used herein. '1 mean a substance adapted to cover the surfaces of metallicparof individual flakes -and preferably to prevent actual surface contact between them during rolling, but still having sufficient lubricatingqualiof disintegration.

ties-that is, viscosity, oiliness etc.-to permit the particles to move during rolling with sumcient freedom to impart a'high polish to their surfaces. When bronze powders for use as paint pigments are to be produced, the aforesaid lubricants must also impart to the powder particles or flakes the ability to leaf" well in paint vehicles, or an additional leafing agent or lubricant capable of imparting this property must be employed. Among the lubricating materials which are most suitable for my purpose are organic compounds of an .unctuous nature, which are usually greases but may be oils. Of these, I generally prefer to use fatty acids, such as stearic, oleic, or ricinoleic acid or a mixture or combination thereof, but glycerides of the fatty acids, such as stearine, tallow or lard oil, are satisfactory and may be used if desired. The particular lubricant selected in any In pplying my process to the production ofaluminum bronze powder flakes, I first prepare shrode by rolling aluminum stock as described in my prior application. or by other-known methods per cent (1%) by weight of a suitable lubricant,

which is intimately mixed with the shrode before or during its reduction or disintegration. The

amount of reduction required, and the conse- -quently required duration of the disintegrating treatment or the number of passes between the.

rolls, vary according to the fineness of the shrode and the desired fineness of the case, however, and in routine operation with known materials and known equipment, it is usu-- ally known in advance. when about of the required reduction of the lubricated shrode has been completed by rolling in a suitable rolling mill or seriesof mills, it is usually desirable to add.

To the shrode I add about one final product," This may be readily determined forany given aomaar another 1% of lubricant, after which the rolling treatment is continued until approximately 50% of the required reduction is completed. This may be when half of the required number of passes between the rolls has been completed, for ex- 5 ample.

After about 50% of the reduction has.been completed, and again when about 75% of the reduction has been completed, it is desirable to make further 1% additions of lubricant. This 10 lubricant should preferably be adapted to im- 1 part good leaflng properties to the powder produced, if the powder is to be used as pigment, whether or not the lubricant added during the first part of the reduction was adapted to act as 16 a leafing agent. Thus I may use stearic acid, for example, throughout the rolling, as it is a satisfactory leafing agent and also a satisfactory lubricant, but I generally prefer to employ ricinoleic acid as the lubricant during the first part 20 of the disintegration, because of its superior lubricating properties which result in' a better cur-'- face-polishing action during the rolling, and permit rolling to the desired thinness without disintegration into granular particles. The additions of 25 ricinoleic acid or other lubricants having a similar effect are accompanied or preferably followed by additions of stearic acid or some other suitable leafing agent. It is to be understood .that my invention is not limited to the specific lubricants which I have mentioned as preferred, and also that the reduction or disintegration need not be carried out in four separate steps as above described. Instead the lubricant may be added continuously during the rolling'treatment, and when more than one kind of lubricant is employed, the lubricants may be mixed and added to the metal particles together, or added alternately as the reduction proceeds. i

The total quantity of lubricant employed may 40 also be varied from the 4% of the weight of shrode or metal particles hereinabove specified.

I have found, however, that substantially that amount of lubricant is generally preferable, especially when fine powder is to be produced. 4 Quantities less than about 4% of the weight of the metal ma not adequately cover the greatly extended s ace of the final product as compared with surfa e of the starting material; and quantities greater than-1% are generally unnecessary and produce no additional advantages. Such larger quantities may usually be used, however, without detriment to the process or product, except that the metal content of the product may be unnecessarily reduced thereby. Sometimes. as when making coarse powders, quantities of lubricant as low as 2% of the weight of the metal give satisfactory results.

. The thoroughness with which the lubricant is applied to and mixed with the shrode or particles .produced therefrom has an important bearing on the quality of the powderproduced, and I have found that it is desirable to spray the lubricant onto the particles or to knead it into them before the material enters the first roll pass, or between successive passes. In any case, it is essential that the metal surfaces be completely covered with lubricating material substantially throughout the rolling treatments which cause disintegration or reduction to the desired size. Whenthis condition is maintained, and rolling is continued-until substantially all of the metal has been disintegrated into flakes of suitable fineties for pigments .or the like, the flakes have well 76 aomeu 3 polished surfaces produced by the continued rubbing in the lubricant.

The pressure applied in the rolling mill is another important factor in determining the quality of the powdered product. Light Pressure during the early stages of rolling facilitates the production of thin flakes, while heavy pressure tends to produce more granular material.

The polished flakes are discharged from the rolling mill in the form of a thin cake held together by the lubricant. This cake is then treated to separate the flakes thereiromin the form of a loose, polished powder, or to produce a pigment paste, either of which may be readily accomplished as will be described hereinbelow.

In order that my invention may be more readily understood, it will nowbedescribed with re!- erence to the accompanying drawing, in which the single figure is a somewhat diagrammatic elevational view, with parts in section, of one form of apparatus suitable for use in my process. In the drawing, a single pair of rolls I is shown, and the shrode 2 or like material to be disintegrated is passed and repassed through these rolls until the desired reduction has been obtained,

but it is obvious that a series of roll pairs or a rolling mills may be employed if desired. The rolls I may have smooth surfaces, or one or both of them may be grooved, as described in my aforementioned copending application, for example. The shrode is fed to the rolls from a storage hopper or analogous container 3 through a chute 5 or other suitable conveying means. Between the rolls l and the hopper 3 a mixing device I may be provided, for thoroughly mixing the metal particles with a lubricant which is supplied to the mixer from a tank or reservoir 8 as required. The mixer I may be of any desired type, such as a revolving drumwith an'in'ternal agitator, or a covered pug mill, or a screw conveyor which may replace the chute 5. The reservoir 8 may be heated, if desired.

The material discharged from the rolls passes through another chute or conveyor l adapted to discharge into a suitable bin or hopper l2. A mixer l3 similar to'the mixer 1 may be provided in this line for intimately mixing the metal particles with a lubricant or a leafing agent or the like, which is supplied from a reservoir It, but

either the mixer 7 or the mixer l3 can usually be omitted. With the use of one or both mixers I y can add the lubricant to the metal particles either continuously or in steps and' thoroughly incorporate it in the resulting cake; or I can incorporate a lubricant in one mixer and another lu bricant or leafing agent in the other.

When using only a single set of rolls l as shown in the drawing, it is necessary to return the ma- I terial first discharged by the rolls for further dis-.

integration. The return of-the material may be efiected in any convenient manner, either manual or mechanical. When a mechanical return system is desired, an elevator is and belt conveyor l1, are-suitable. The elevator may receive material from the chute ID or the bin 12, and may have the form of v a bucket conveyor or a screw conveyor, for example. When the shrode has been suitably combined with lubricant and/or leafing agent and passed through the rolls until the desired disintegration has been effected, the product in the form of a cakeor thick mixture of fine, polished, flake-like particles of bronze powder I9 is allowed to accumulate in the bin E2 or some other suitable reservoir.

The further treatment of the cake l9 depends on the form in which it is desired to obtain the powder, it is necessary to. apply a treatment to remove excess lubricant. This can be done conveniently and economically by mixing-the cake with a suitable volatile solvent in a revolving drum 2| provided with a roll agitator 22 or other equivalent apparatus. The solvent is supplied 10 in controlled quantities from a reservoir 23, and

is preferably an organic liquid such as ether, acetone, or t'oluol, which is capable of dissolving the lubricant without reacting with the powder particles. When solution of the lubricant is substantially complete, the fluid suspension is discharged from the drum 2| or'other dissolving vessel into a tank 25 connected with an atomizing nozzle '26 provided with a compressed air connection 27, or the atomizer is connected directly to the drum 2|, and the suspension is. sprayed into a chamber 28, which is preferably heated. The solvent and a part of the lubricant volatilize and pass from the chamber 28 through a suitable condenser 30, where they are recovered. Evaporation of the solvent leaves a coating of lubricant on the surfaces of the flakes, so that the leafing property and polish are'retained, but the flakes deposit in the chamber in loose powder form and are suitable for use as a pigment or for other purposes.

I have found that in addition to removing excess lubricant from the cake by dissolving and then separating the powder from the solvent by evaporation as previously described, or otherwise, .85 treatments of a mechanical nature may be employed to separate the flakes from the cake. For example, the cake withdrawn from the hopper l2 may be gently tumbled in a revolving drum 2| with an inert solid granular material, such as 40 I the like, operated in known manner, and is ready for use as pigment or otherwise. The sand can be freed from lubricant, as by washing in a solvent, and re-used if desired.

While my invention is advantageously used in the production of loose bronze powder for pigments or the like, it-has an especially advantageous application in the production of bronze powder pigment pastes. Such pastes are preferred 'to the loose powder for some purposes, as is well known, and in the past the demand for a paste product has frequently been'satisfied by preparing a loose powder and then mixing it withenough vehicle to form a paste of the desired consistency. This is often slow and laborious, and therefore expensive, as the polished powder is not, always wettable; and it is difficult to produce a product of uniformly high quality. By the process of my present invention, a pigment-paste of high quality is uniformly and lating through the rolls I when disintegration has been completed or substantially completed :and the desired "cake has been produced. This may be readily'done by meansof one of the mixers I and i3, to which the mineral spirits is supplied from the corresponding tank 8 or I. Paste is then collected in thestorage hopper l2, and the subsequent apparatus can be eliminated. If it is desired to remove some of the lubricant contained in the cake, this may be readily done by a slight modification of the method previously described. The mineral spirits or other solvent or diluent is then added to the cake in the revolving drum 2|, or its equivalent, in a quantity more than sufiicient to loosen the cake,

and agitated to form a relatively thin slurry. This may be allowed to stand, whereupon the flakes settle, and the excess solvent containing some of the lubricant is decanted off, leaving a paste. The slurry may also be separated in a filter press or centrifuge, and similar methods may be employed-for the recovery of loose powder by the solution method. While I prefer to employ mineral spirits as the solvent or thinner for the production of pigment pastes, solvent naphtha or turpentine or the like may also be used.

It will now be readily understood that my process-offers many advantages over processes previously employed or proposed, in that the capacity of a properly operated rolling mill for distintegration or reduction, of shrode and the like is much greater than the capacity .of a stamp mill, for example; and in that the cake which I obtain as an intermediate product is a convenient material for the production of high grade polished bronze powders, and especially for the production of bronze powder pastes; and in other respects. While my invention has been described and illustrated with special reference to embodiments thereof which are now pre-.

ferred, it is to be understood that certain other modifications and embodiments may be made without departing fromthe spirit of my inven-.

tion, and within the scope ofthe appended claims.

I claim:

1. In a process of preparing aluminum bronze pigment, the distintegrating step comprising repeatedly rolling aluminum covered with a lubricant to form a cake of fine aluminum flakes held together by the lubricant.

2. In a process of preparing aluminum bronze pigment, the step comprising repeatedly rolling pieces of aluminum coatedwith a lubricating material adapted to prevent welding of pieces which overlap to disintegrate the aluminum into flakes and to form therefrom a thin cake-held together by the lubricating material,

3. The process of preparing aluminum bronze pigment, which comprises repeatedly rolling aluminum material coated. with a lubricant to apr'zsal out very rapidly in the revolving drum 2| proform fine flakes of aluminum bronze powder held together in the form of a cake by the lubricant. and separating the flakes from saidcake.

- 4.. In a process of preparing aluminum bronze pigment; the combination of steps comprising 6 the material into fine flakes-of aluminum bronze powder held together in the form of a cake by the lubricant, and dissolving the lubricant to 10 separate the flakes from the cake.

5. The process of preparing aluminum bronze pigment, which comprises repeatedly rolling aluminum material coated with a lubricant to disintegrate the material into fine flakes of 15 aluminum bronze powder held together in the form of a cake by the lubricant, and mechanically separating the flakes from the cake.

' 6. The process of preparing aluminum bronze pigment, comprising repeatedly rolling aluminum material coated with a lubricant to distegrate the material into fine flakes of aluminum bronze powder held together in the form of a cake by the lubricant, and agitating the cake with an inert granular material to separate said flakes 25 therefrom. w g

'7. The process of preparing aluminum bronze pigment, which comprises disintegrating alumi- 8. The process of preparing aluminum bronze 35 pigment, which comprises repeatedly rolling thin aluminum material with a lubricant to distintegrate the aluminum into fine flakes held together in the form of a cake by the said lubricant, agitating the cake with asolvent to dissolve at least a part of the lubricant and to loosen flakes from the cake, and separating loosened flakes of bronze powder from solvent containing dissolved lubricant.

-9. The process a! preparing aluminum bronze powder, which comprises repeatedly rolling thin aluminum material with a lubricant to disintegrate the aluminum into fine flakes held together in the form of a cake by the said lubricant, agitating the cake with a solvent to dissolve at least a part of the lubricant and to form a suspension of loosened flakes of bronze powder, spraying the suspension into a chamber to evaporate solvent, and collecting the loosened flakes of bronze powder.

10. The process of manufacturing aluminum bronze powder, comprising coating thin aluminum with a lubricant and-disintegrating the aidminum by repeated rolling to form fine flakes of 60 aluminum bronze powder held together in the form of a cake by the lubricant, separating the flakes from the cake by agitating with solid inert particles heavier than the aluminum flakes and adapted to remove lubricant therefrom, and airseparating the bronze powder flakes from the inert particles.

11. The process of manufacturing aluminum bronze powder pastes, which comprises coating 70 thin aluminum material with an unctuous organic lubricant. and repeatedly rolling it to disintegrate the aluminum into fine flakes held together in the form of a cake by the lubricant, adding at least sufiicient diluent to loosen the 75 cake, and subjecting the mixture to further rollins.

-12. The process of manufacturing aluminum integrate .the aluminum into fine flakes held together in the form of a cake by the lubricant, adding a diluent capable of dissolving the lubricant, in a quantity more than sufiicient to loosen the cake, agitatingto dissolve lubricant, and withdrawing excess diluent with lubricant dissolved therein.

13. In a process of producing aluminum bronze pigment, the step comprising repeatedly rolling aluminum material with an organic lubricant to disintegrate the material into finely divided flakes of bronze powder with a finished polish and good leafing properties held together in the form of a cake by the lubricant.

14. In a process of producing aluminum bronze pigment, the combination of steps comprising mixing thin aluminum material with a lubricant, rolling to disintegrate the aluminum, adding more lubricant, and repeating the rolling and additions of lubricant to complete the disintegration and form fine polished flakes of bronze powder held together in the form of a cake by the lubri-.

erties to the disintegrated aluminum, and continuing the rolling to form fine polished flakes of bronze powder with good leafing properties held together in the form of a cake by the lubricant.

16. In a process of producing aluminum bronze pigment, the step comprising rolling thin pieces of aluminum with about 4% by weight 01 a lubricant to disintegrate the aluminum into fine flakes held together in the form or a cake by the lubricant.

17. In a process of producing aluminum bronze pigment, the step comprising rolling thin pieces 5 of aluminum with about 4% by weight of a lubricant adapted to impart good leafing properties to the pigment to disintegrate the aluminum into fine flakes held together in the form of a cake by the lubricant. 10 18. In a process of producing aluminum bronze pigment, the step comprising rolling thin pieces of aluminum with about 4% by weight of a lubricant containing stearic acid to disintegrate the .acid, and continuing the rolling to disintegrate the aluminum into fine polished flakes having good leafing properties and held" together in the form of a cake by the organic acids. 30 21. As a new product, fine polished flakes of aluminum bronze powder held together in the form of a cake by unctuous organic lubricating material.

22. As a new product, fine poiishedflakes of 35 aluminum bronze powder having good leafing properties and held together in ;the form of a cake by lubricating material'comprising stearic acid and ricinoleic acid, said lubricating material being present in an amount equal to about 4% 40 of the weight of the powder.

DALE M. BOOTHMAN. 

